Micromachined devices include devices, such as actuators and motors, in which a movable element is required to move substantially linearly with respect to another element. Such devices include a suspension that supports the movable element relative to the other element. Desirable properties of the suspension include that the suspension allow a broad range of substantially linear movement and that the suspension have a high compliance in the direction of travel of the movable element. A high compliance reduces the force that a motor needs to generate to move the movable element.
An electrostatic or electromagnetic motor used to move the movable element in its direction of travel not only generates a force in the direction of travel, but additionally generates parasitic forces in directions orthogonal to the direction of travel. More than minimal motion of the movable element in a direction orthogonal to the direction of travel is undesirable since it can result in physical contact between the movable element and the other element. Accordingly, another desirable property of the suspension is that it should be have a low compliance in at least one direction orthogonal to the direction of travel.
One form of suspension commonly used in micromachined devices is known as a flexural device. Flexural devices are based on elongate flexible beams. Such beams can have a cross-sectional shape with a highly-asymmetrical aspect ratio. Flexural devices incorporating such flexible beams inherently have a high compliance in the direction in which their cross section is narrow and inherently have a low compliance in the direction in which their cross-section is wide. Thus, flexural devices based on flexible beams having a narrow cross-section in the direction of travel, which will be called the x-direction, and having a wide cross-section in the z-direction orthogonal to the x-direction inherently have a high compliance in the direction of travel and inherently have a low compliance in the z-direction. Alternatively, in applications in which some motion in the z-direction is allowable, the flexible beams can be formed with a cross-sectional shape having a less asymmetrical, or even a symmetrical, aspect ratio.
In the y-direction, orthogonal to both the x- and z-directions, flexural devices based on elongate flexible beams have a low compliance when the flexible beams are straight, i.e., not bent. Typically, the flexible beams are straight in the rest position of the movable element. The y-direction compliance increases as the flexible beams bend lengthways with increasing displacement of the movable element in the x-direction from its rest position. This compliance vs. displacement characteristic is undesirable, as it limits the practical range of motion of the movable element in the x-direction. Motion beyond the point at which the y-direction compliance of the flexural device increases beyond a threshold related to the y-direction parasitic force can result in catastrophic run-away motion in the y-direction.
What is needed, therefore, is a flexural device-based suspension for micromachined devices that has a high compliance in a direction of travel of the movable element and a low compliance in at least one direction orthogonal to the direction of travel. The suspension should maintain its low compliance in the orthogonal direction over a substantial range of movement of the movable element in the direction of travel. What is also needed is a suspension having a structure capable of easily fabrication using conventional micromachining techniques.
The invention provides a flexural device-based suspension for suspending a movable element with high compliance in a direction of travel and low compliance in a direction orthogonal to the direction of travel. The suspension comprises two flexural devices and a constraining element. The two flexural devices are connected to the movable element. Each of the flexural devices includes an elongate floating beam disposed substantially parallel to the direction of travel. The constraining element is for constraining relative motion of the floating beams in the direction of travel and for allowing the floating beams to move freely relative to one another in the orthogonal direction.
When the movable element moves in the direction of travel, the floating beams move relative to one another in the orthogonal direction. Undesired motion of the movable element in the orthogonal direction causes the floating beams to move relative to one another in the direction of travel. Thus, by constraining relative motion of the floating beams in the direction of travel while allowing the floating beams to move freely relative to one another in the orthogonal direction, the constraining element resists undesired motion of the movable element in the orthogonal direction while allowing the movable element to move freely in the direction of travel.
The invention also provides a micromachined device that comprises a movable element, a first flexural device, a second flexural device and a constraining element. The first flexural device and the second flexural device are located on opposite sides of the movable element and permit movement of the movable element in a direction of travel. Each of the flexural devices includes an elongate floating beam substantially parallel to the direction of travel. The constraining element extends between the floating beams, and has a low compliance in the direction of travel and a high compliance in a direction orthogonal to the direction of travel.
The low compliance of the constraining element in the direction of travel resists relative motion of the floating beams in the direction of travel, while its high compliance in the orthogonal direction allows the floating beams to move freely relative to one another in the orthogonal direction. Thus, the constraining element resists undesired motion of the movable element in the orthogonal direction while allowing the movable element to move freely in the direction of travel.
Other features and advantages of the invention will be apparent upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.